1. Field of the Present Invention
The present invention relates to a driving device having an extremely compact size, and a light amount controller and a shutter using the driving device.
2. Description of the Related Art
Conventionally, motors that can be designed compact in size include a brushless motor. Brushless motors with simple driving circuits include a stepper motor, described below.
FIG. 17 shows an example of a small-sized hollow cylindrical stepper motor. The stepper motor includes two stators 102 each comprised of a bobbin 101 having a stator coil 105 concentrically wound thereon, two stator yokes 106 axially fixedly holding the bobbin 101 in a sandwiching fashion, the stator yokes 106 each having stator teeth 106a and 106b alternately arranged circumferentially of an inner peripheral surface of the bobbin 101, and a casing 103 to which are secured the stator yokes 106 formed integrally with the respective stator teeth 106a and 106b. One of the two casings 103 has a flange 115 and a bearing 108 fixed thereto, while the other casing 103 has another bearing 108 fixed thereto. A rotor 109 is comprised of a rotor magnet 111 rigidly fitted on a rotor shaft 110. The rotor magnet 111 defines radial gaps between the same and the stator yokes 106 of the stators 102. The rotor shaft 110 is rotatably supported by the two bearings 108 on opposite ends thereof.
A light controller using a variation of the stepper motor constructed as above has been proposed in Japanese Patent Publication (Kokoku) No. 53-2774. The light controller controls the quantity of passing light by opening and closing shutter blades connected to the stepper motor, in a stepwise fashion. Another variation is a hollow motor proposed in Japanese Laid-Open Patent Publication (Kokai) No. 57-166847. The hollow motor is a ring-shaped stepper motor which allows light to pass through a cavity formed in a central portion thereof.
There are known digital cameras of a kind which use a CCD or the like as an image pickup device for photoelectrically converting an object image to thereby record the image on a storage medium as information of a still image. The digital cameras of this kind include a type having a diaphragm blade and a shutter blade, and actuators for actuating the respective blades.
Operations related to exposure of the digital camera of the above-mentioned type are as follows.
First, when the main power supply is turned on to make the image pickup device operative before photographing, the shutter blade is held in its open position which allows the image pickup device to be exposed to light. The image pickup device repeatedly accumulates, discharges, and transfers electric charge to allow an object field to be observed on an image monitor. When a release button is depressed, a diaphragm value and an exposure time are determined according to an output from the image pickup device at this time point. Judging from the determined diaphragm value and exposure time, if it is necessary to reduce the diameter of an exposure aperture, first, the diaphragm blade is operated into a position providing a predetermined diaphragm value. Then, the image pickup device from which the stored electric charge has been discharged is caused to start storage or accumulation of electric charge in response to a storage start signal. At the same time, an exposure time control circuit is started in response to the storage start signal serving as a trigger signal, and when the lapse of the predetermined exposure time has been counted up, the shutter blade is actuated into a closed position for blocking light to the image pickup device. After the blocking of light to the image pickup device, the stored electric charge is transferred, whereby image information is recorded onto a storage medium via an image writing device. The exposure of the image pickup device is inhibited during the transfer of the electrical charge because it is necessary to prevent the charge from being changed by extra light.
Another type of digital camera has been proposed in Japanese Laid-Open Patent Publication (Kokai) No. 11-305285, in which a diaphragm blade and a shutter blade are driven by a single actuator. In this digital camera, the actuator can assume any of three states, i.e. a deenergized state, a normally energized state, and a reversely energized state. When the actuator is in the deenergized state, the camera is placed in an intermediate aperture state. When the actuator is in the normally energized state, the camera is placed in a maximum aperture state, while when the actuator is in the reversely energized state, the camera is placed in a fully closed state.
In the above conventional small-sized stepper motor shown in FIG. 17, however, the cases 103, the bobbins 101, the stator coils 105 and the stator yokes 106 are concentrically arranged around the rotor 109, which inevitably results in increased outer dimensions of the motor. Further, magnetic flux generated by energization of the stator coils 105 mainly flows between the end faces 106a1 of the stator teeth 106a and the end faces 106b1 of the stator teeth 106b as shown in FIG. 18, and hence the magnetic flux does not effectively act on the rotor magnet 111.
Similarly, the light controller proposed in Japanese Patent Publication (Kokoku) No. 53-2774 and the hollow motor proposed in Japanese Laid-Open Patent Publication (Kokai) 57-166847 each have stator coils and stator yokes arranged around a rotor magnet, so that the outer dimensions of the motor are increased, and magnetic flux generated by energization of the stator coils does not effectively act on the rotor magnet.
Further, a coin-shaped brushless motor as shown in FIG. 19 has been proposed e.g. in Japanese Laid-Open Patent Publications (Kokai) No. 7-213041 and No. 2000-50601. The brushless motor is comprised of a plurality of coils 301, 302, 303 and a disk-shaped magnet 304. As shown in FIG. 19, each of the coils has a thin coin-like shape, and is disposed such that the axis thereof extends parallel with that of the magnet. The disk-shaped magnet is magnetized in the axial direction thereof, and is disposed such that the magnetic surface (inner peripheral surface) of the magnet faces in a direction perpendicular to the axis of each of the coils.
In this motor, as illustrated by arrows in FIG. 20, magnetic flux generated by the coils cannot fully effectively act on the magnet. Further, the center of a rotational force or torque generated by the magnet is away from the outer periphery of the motor by a distance of L, so that the torque generated by the motor is small for the size of the motor. In addition, a central portion of the motor is occupied by the coils and the magnet, it is difficult to utilize this portion for some other purposes.
Further, some shutter devices for digital cameras have diaphragm blades and shutter blades incorporated therein. In view of costs and space, it is preferable that these blades are actuated by a single actuator. Japanese Laid-Open Patent Publication (Kokai) No. 11-305285 discloses a shutter device of this type in which a single actuator actuates a shutter blade which also serve as a diaphragm blade. However, in the shutter device, a magnetic neutral point thereof is utilized to control the position of the shutter blade for an intermediate aperture, which makes it difficult to operate the blade with high accuracy.
It is a first object of the present invention to provide a small-sized and slim driving device which is easy to manufacture and capable of producing high output.
It is a second object of the present invention to provide a light amount controller using a small-sized and slim driving device which is easy to manufacture and capable of producing high output.
It is a third object of the present invention to provide a shutter using a small-sized and slim driving device which is capable of changing a diaphragm value and capable of producing high output.
It is a fourth object of the present invention to provide a shutter which is capable of holding its open state or closed state even when the device is not energized, thereby reducing power consumption.
To attain the first object, in a first aspect of the present invention, there is provided a driving device comprising a magnet having a hollow cylindrical shape and having an outer peripheral surface and an inner peripheral surface, at least the outer peripheral surface being circumferentially divided into n sections magnetized so as to have alternately different poles, the magnet being rotatable about a rotational axis of the hollow cylindrical shape thereof, a coil arranged axially of the magnet and parallel thereto, an outer magnetic pole portion disposed to be magnetized by the coil, the outer magnetic pole portion having a plurality of hair comb tooth-shaped portions opposed to the magnet and arranged around the magnet such that an angle corresponding to a circumferential width of each of the hair comb tooth-shaped portions opposed to the magnet about the rotational axis of the hollow cylindrical shape of the magnet is equal to a predetermined angle A, and an inner magnetic pole portion disposed to be magnetized by the coil, the inner magnetic pole portion having a hollow cylindrical shape opposed to the inner peripheral surface of the magnet, wherein the predetermined angle A is set to such a value that a rotational force acts on the magnet to return to a position in which a circumferential center of each of n magnetized sections on the outer peripheral surface of the magnet is opposed to a circumferential center of a corresponding one of the hair comb tooth-shaped portions of the outer magnetic pole portion, when the circumferential center of each of n magnetized sections shifts from the position.
To attain the second object, in a second aspect of the present invention, there is provided a light amount controller comprising a magnet having a hollow cylindrical shape and having an outer peripheral surface and an inner peripheral surface, at least the outer peripheral surface being circumferentially divided into n sections magnetized so as to have alternately different poles, the magnet being rotatable about a rotational axis of the hollow cylindrical shape thereof, a coil arranged axially of the magnet and parallel thereto, an outer magnetic pole portion disposed to be magnetized by the coil, the outer magnetic pole portion having a plurality of hair comb tooth-shaped portions opposed to the magnet and arranged around the magnet such that an angle corresponding to a circumferential width of each of the hair comb tooth-shaped portions opposed to the magnet about the rotational axis of the hollow cylindrical shape of the magnet is equal to a predetermined angle A, and an inner magnetic pole portion disposed to be magnetized by the coil, the inner magnetic pole portion having a hollow cylindrical shape opposed to the inner peripheral surface of the magnet, and a light amount control member which can be opened or closed in a manner interlocked to the magnet to thereby control an amount of light passing through the inner magnetic pole portion, wherein the predetermined angle A is set to such a value that a rotational force acts on the magnet to return to a position in which a circumferential center of each of n magnetized sections on the outer peripheral surface of the magnet is opposed to a circumferential center of a corresponding one of the hair comb tooth-shaped portions of the outer magnetic pole portion, when the circumferential center of each of n magnetized sections shifts from the position.
To attain the second object, in a third aspect of the present invention, there is provided a light amount controller comprising a magnet having a hollow cylindrical shape and having an outer peripheral surface and an inner peripheral surface, at least the outer peripheral surface being circumferentially divided into n sections magnetized so as to have alternately different poles, the magnet being rotatable about a rotational axis of the hollow cylindrical shape thereof, a coil arranged axially of the magnet and parallel thereto, an outer magnetic pole portion disposed to be magnetized by the coil, the outer magnetic pole portion having a plurality of hair comb tooth-shaped portions opposed to the magnet and arranged around the magnet such that an angle corresponding to a circumferential width of each of the hair comb tooth-shaped portions opposed to the magnet about the rotational axis of the hollow cylindrical shape of the magnet is equal to a predetermined angle A, and an inner magnetic pole portion disposed to be magnetized by the coil, the inner magnetic pole portion having a hollow cylindrical shape opposed to the inner peripheral surface of the magnet, a light amount control member which can be opened and closed in a manner interlocked to the magnet to thereby control an amount of light passing through the inner magnetic pole portion, and control means for controlling the light amount control member by switching a direction of energization of the coil such that the magnet is switched between a first state in which the magnet is held at a first rotational position by attractive forces of the magnet and the outer magnetic pole portion when the coil is deenergized and a second state in which the magnet is held at a second rotational position to which the magnet has been rotated through a predetermined angle from the first state, by attraction forces of the magnet and the outer magnetic pole portion when the coil is deenergized, wherein the predetermined angle A is set to such a value that a rotational force acts on the magnet to return to a position in which a circumferential center of each of n magnetized sections on the outer peripheral surface of the magnet is opposed to a circumferential center of a corresponding one of the hair comb tooth-shaped portions of the outer magnetic pole portion, when the circumferential center of each of n magnetized sections shifts from the position.
In the first to third aspects of the present invention, preferably, assuming that the magnet has an outer diameter of D1 and an inner diameter of D2, the predetermined angle A is set to satisfy a condition defined by an expression:
A less than (248.4/n)xe2x88x9258.86xc3x97(D1xe2x88x92D2)/(D1xc3x97xcfx80).
In the first to third aspects of the present invention, preferably, each of the hair comb tooth shaped portions of the outer magnetic pole portion has an axial length larger than a height of the outer peripheral surface of the magnet.
In the first to third aspects of the present invention, preferably, the driving device or the light amount controller includes a light amount controller including a rotation-preventing member for limiting a rotational angle of the magnet.
In the first to third aspects of the present invention, preferably, the magnet is rotatable through a rotational angle range smaller than an angle corresponding to a circumferential length of each of the n sections having alternately different poles about the rotational axis of the hollow cylindrical shape of the magnet.
To attain the third and fourth objects, in a fourth aspect of the present invention, there is provided a shutter comprising a magnet having a hollow cylindrical shape and having an outer peripheral surface and an inner peripheral surface, at least the outer peripheral surface being circumferentially divided into n sections magnetized so as to have alternately different poles, the magnet being rotatable about a rotational axis of the hollow cylindrical shape thereof, a coil arranged axially of the magnet and parallel thereto, an outer magnetic pole portion opposed to the outer peripheral surface of the magnet, to be magnetized by the coil, an inner magnetic pole portion having a hollow cylindrical shape opposed to the inner peripheral surface of the magnet, to be magnetized by the coil, a shutter blade interlocked with the magnet for moving between a closing position for closing an optical path formed by an inside of the hollow cylindrical shape of the inner magnetic pole portion and an opening position for holding the optical path in an open state, and light amount-adjusting means for changing an amount of light passing through the optical path in a manner interlocked with rotation of the magnet.
Preferably, the light amount-adjusting means comprises a one-way clutch having an input side thereof connected to the magnet, and an output side, for transmitting only a rotational force of the magnet in a predetermined direction to the output side thereof, and a light amount-adjusting member connected to the output side of the one-way clutch for entering into or retracting from the optical path in a manner interlocked to motion of the output side of the one-way clutch to thereby change the amount of light passing through the optical path.
Preferably, assuming that the n sections of the outer peripheral surface of the magnet have n alternately different poles, the outer magnetic pole portion opposed to the outer peripheral surface of the magnet has a shape of a plurality of hair comb tooth-shaped portions arranged circumferentially at equal intervals of an integral number of times as large as 720/n degrees around the outer peripheral surface of the magnet, each of the hair comb tooth-shaped portions of the outer magnetic pole portion opposed to the outer peripheral surface of the magnet having a circumferential width corresponding to a predetermined angle A about a rotational axis of the hollow cylindrical shape of the magnet, the predetermined angle A being set to such a value that a rotational force acts on the magnet to return to a position in which a circumferential center of each of n magnetized sections on the outer peripheral surface of the magnet is opposed to a circumferential center of a corresponding one of the hair comb tooth-shaped portions of the outer magnetic pole portion, when the circumferential center of each of n magnetized sections shifts from the position.
In the fourth aspect of the present invention, preferably, assuming that the magnet has an outer diameter of D1, and an inner diameter of D2, the predetermined angle A is set to satisfy a condition defined by the following expression:
A less than (248.4/n)xe2x88x9258.86xc3x97(D1xe2x88x92D2)/(D1xc3x97xcfx80).
According to the first to third aspects, the outer diameter of the driving device is determined by the outer magnetic pole portion opposed to the outer peripheral surface of the magnet, the inner diameter of the driving device is determined by the inner magnetic pole portion opposed to the inner peripheral surface of the magnet, and the axial height of the driving device is determined by the axial arrangement of the coil and the magnet. As a result, it is possible to largely reduce the size of the driving device. Further, the magnetic flux generated between the outer magnetic pole pieces and the inner magnetic pole portion magnetized by excitation of the coil crosses the magnet arranged between the magnetic pole pieces and member, and hence effectively acts on the magnet.
Furthermore, assuming that the angle corresponding to the circumferential width of each hair comb tooth-shaped portion of the outer magnetic pole portion opposed to the magnet about the rotational axis of the hollow cylindrical shape of the magnet is equal to the predetermined angle A, and the magnet has n magnetized poles, an outer diameter of D1 and an inner diameter of D2, the value A is set to satisfy the condition defined by the expression of A less than (248.4/n)xe2x88x9258.86xc3x97(D1xe2x88x92D2)/(D1xc3x97xcfx80) holds. Therefore, when the coil is not energized, the center of each magnetized pole of the magnet can be stably held at a position opposed to the center of a corresponding hair comb tooth-shaped portion of the outer magnetic pole portion.
Moreover, since each comb hair tooth-shaped portion of the outer magnetic pole portion is configured to have an axial length larger than the height of the outer peripheral surface of the magnet, a force axially exerted on the magnet by the outer magnetic pole portion and the inner magnetic pole portion is reduced. As a result, sliding friction between the magnet and members holding the magnet in the axial direction is reduced, which enables smooth rotation of the magnet.
Further, the light amount controller according to the second and third aspects of the present invention includes the above driving device, and the light amount control member connected to the magnet of the driving device, for pivotal motion for control of the amount of light passing through the inside of the hollow cylindrical inner magnetic pole portion, it is possible to allow light to pass through the central portion of the driving device.
According to the third aspect of the present invention, it is possible to switch the light amount control between two states by switching the direction of energizing the coil. Further, when the coil is deenergized, the magnet is held at either of the two states. Thus, even if the coil is not energized, the light amount control member is prevented from being moved due to a shock or the like, which makes it possible to enhance reliability of the light amount controller and reduce power consumption.
Further, according to the fourth aspect, since the outer diameter of the motor is determined by the outer magnetic pole piece opposed to the outer peripheral surface of the magnet, and the axial length of the motor is determined by the axial arrangement of the coil and the magnet, it is possible to largely reduce the size of the driving device. In addition, magnetic flux generated by the outer and inner magnetic pole portions by excitation of the coil crosses the magnet arranged therebetween, and hence effectively acts on the magnet.
Moreover, according to the arrangement that the shutter is provided with shutter blades and the light amount control member, which are connected to the magnet for pivotal motion, the shutter can be configured such that light is allowed to pass through the central portion of the driving device.
Further, since the light amount-adjusting means is operated in a manner interlocked with rotation of the magnet, for changing the amount of light passing through the optical path, the shutter can have a plurality of diaphragm values.
Furthermore, according to the arrangement that the shutter has light amount control means that takes out only rotation of the magnet in one direction to thereby change the amount of light passing through the optical path, it is possible to carry out an operation for changing the diaphragm value and an operation for opening/closing the shutter by a single actuator, which contributes to reduction of the size thereof. In addition, by rotating the magnet alternately in normal and reverse directions before exposure for actually capturing an image onto a recording medium, the light amount-adjusting means can be selectively driven into a plurality of light amount control states according to the number of times of the rotation.
The above and other objects, features, and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompany with drawings.